1. Field of the Invention
The invention relates to a vacuum conveyor for guiding a running web, e.g., a lead strip (or "threading tail"). Such a vacuum conveyor is used for transporting a web, e.g. a paper and cardboard web, from a section of a paper-making or paper-finishing machine to a following section of that machine.
2. Discussion of Background Information
A vacuum conveyor is known from DE 26 36 887 which is similar to U.S. Pat. No. 4,022,366. Conveyors of this kind have proven successful in operation. In some applications, however, a paper tail must be transferred from a vacuum conveyor to a rope nip (of a following machine section) at a very high speed (over 1500 meters/min). This requires a very rapid change of degree of the vacuum applied to the conveyor. For this purpose it is known to use a pneumatic operated damper at the vacuum source or in the vacuum line.
Recently, however, the operating speed of paper-making or paper-finishing machines is being further increased, namely up to about 2200 meters/min. Unfortunately, in such extreme high speed systems, the conventional dampers do not operate in a reliable manner.